Biology 201 Dr. Edwin DeMont Molluscan Success St. Francis Xavier University

Molluscs Filmed live Members of this very diverse group range in size from a few mm to the 18 meter giant squid. Giant squid A land gastropod St. Francis Xavier University

1. A body composed of a head-foot and visceral mass. Molluscs Molluscs are triploblastic and have bilateral symmetry, but they also have 3 unique features. 1. A body composed of a head-foot and visceral mass. 2. A mantle that encloses the visceral mass, secretes the shell (if present), and forms the mantle cavity. 3. A radula, a rasping structure used in feeding is usually present. The radula has been lost in the bivalves. St. Francis Xavier University

Class Gastropoda ~ 35,000 species – the most of any molluscan class. Molluscs Class Gastropoda ~ 35,000 species – the most of any molluscan class. Class Bivalvia includes clams, mussels, oysters and scallops, and is the second largest molluscan class (30,000 described species). Class Cephalopoda, including octopuses, squid, cuttlefish, and the nautilus, contains the most morphologically complex invertebrates, particularly with respect to the nervous system. Loligo @ MBL St. Francis Xavier University

Squid swimming Muscular mantle Water Radial ‘elastic’ fibers Escape response – refilling powered by radial muscle contraction. Muscular mantle Normal swimming – refilling powered by an elastic mechanism. Water Radial ‘elastic’ fibers Radial muscle fibers Squid also have fins. Video St. Francis Xavier University

Sessile bivalve- like the mussel in lab Bivalve Anatomy Bivalves are laterally compressed and covered by two valves, or shell halves. However, the shell is a single structure with a hinge region. A pair of adductor muscles keeps the shell closed. Muscle antagonism? Morphology of swimming scallops is specialized – we will study in the laboratory. Sessile bivalve- like the mussel in lab St. Francis Xavier University

Scallops swim with jet propulsion - thought to be an escape response. Scallop Swimming Scallops swim with jet propulsion - thought to be an escape response. Image source 3. Jets formed 1. Muscle contracts 4. Scallop moves forward 2. Mantle velum seals gap Click on picture for video St. Francis Xavier University

Bivalves are typically sedentary filter feeders. Bivalve Feeding Bivalves are typically sedentary filter feeders. Filter feeding is accomplished by the lamellae of the gills. Gills are used in both respiration and feeding. St. Francis Xavier University

Filter Feeding A physical process which involves very small particles moving through a fluid at low velocities. Video of viscosity Small The behaviour of particles in this physical world is different than our world – it is dominated by viscosity (the ‘stickness of a fluid’). Large Small particles in water moving at low velocity ‘see’ a very viscous world. Click on photos for video Large particles in water moving at high velocity ‘see’ a very inertial world. St. Francis Xavier University

Reynolds number The type of physical world an object in a fluid experiences can be described by the Reynolds number: Inertia forces ------------------ Viscous forces High Re = whale → inertia → keeps moving. Low Re = sperm → viscosity → stops immediately. St. Francis Xavier University

Reynolds number Two very different types of flow exist in fluids, and the type of flow depends on the Reynolds number: Laminar flow Turbulent flow Click on photo for video Nature of interactions of the object moving through the fluid is different depending on what type of flow exists. St. Francis Xavier University

Dark arrows – motion after filtering Bivalve Feeding Cilia move water into the mantle cavity through the incurrent aperture and it exits through the excurrent aperture. Collected food is directed to the cilia-covered labial palp surrounding the mouth. The labial palps sort the food and then direct it into the stomach. Dark arrows – motion after filtering Video by Ward and colleagues St. Francis Xavier University

On Growth Cones exhibit isometric growth Other animals exhibit allometric growth. Animals add more material at the free edge and ‘grow’. What about growth in other animals? Exoskeletons? Endoskeletons? From: Vogel, S. (2003) Comparative Biomechanics: Life’s Physical World. Princeton University Press. St. Francis Xavier University